Replacement spiral balance and shoe
I cannot remove the shoes, but they appear to be 2-1/8" in height, 1-3/8" wide, and 1/2" deep. The slot is approximately 3/16 x 3/8.
I see there are two ways to remove the shoes: cut into the vinyl or use a spreader. I'm more inclined to use the spreader but am concerned if it will work when the window is sandwiched by walls.
Hello there. Some of these older spiral balances use those white plastic outer tubes, which can become flimsy over time and become hard to measure the diameter of. I would get a few readings on different spiral balances throughout the house. If they all out to below 7/16", or outright 3/8", most likely it is the Series 900. Just do your best to get enough readings.
The tip was likely an outmoded white rating. To know what color tip you need, weigh the window sash that the spiral balance supports. You can use that weight to choose the right color tip option.
Finally, the pivot shoe is likely the 15-188 or 15-178, but removing it to get as accurate a thickness reading as possible would be advisable.
Finally, the 75-069 Jamb Spreaders are certainly an option. It's tough to say if it'd be too tight a fit with these windows. If you do wish to form a 'cutout' instead, see the video below.